1. Field of the Invention
The present invention relates to improvements in a temperature-controlled fan fluid coupling which is generally used with an automotive engine to drive the cooling fan in such a way that cooling air is supplied to the engine always at a flow rate corresponding to the operating conditions of the engine. That is, the invention relates to a fan fluid coupling which automatically controls the flow rate of cooling air supplied to an automotive engine.
2. Description of the Prior Art
A conventional fan coupling of this kind is shown in FIG. 5, where a partition plate 14 is provided with a circular outflow-adjusting hole 14'. The plate contains a resilient valve member 15 in the form of a plate. The valve member interlocks with an interlocking rod which follows deformation of a temperature-sensing device mounted outside. The temperature-sensing device deforms as temperature varies. The valve member 15 has a flat surface at its front end. As temperature varies, the flat surface of the valve member 15 moves forward or rearward to close or open the hole 14'. The characteristic of this fan coupling is indicated by curve (B) in FIG. 6.
In this conventional fan coupling, the outflow-adjusting hole 14' is closed or opened directly by the flat surface at the front end of the valve member 15 which moves forward or rearward. Therefore, the area of the hole 14' when it is fully open is restricted by the width of the valve member 15. For this reason, it is impossible to make the area of the hole large. Further, if a slight rift is created in the valve member, the effective area with which oil passes varies greatly. Consequently, the amount of oil delivered cannot be controlled accurately. As can be seen from the characteristic curve (B), the rotational speed increases rapidly at a temperature of about 60.degree. under normal operating conditions. Hence, the fan coupling is unable to constantly supply adequate amount of cooling air over a wide range of temperatures when the vehicle is running. Thus, noise generated by the fan, consumption of the energy, and the time for which the automotive engine is warmed up cannot be reduced sufficiently. Furthermore, because only the long, integrated valve member 15 is used, the valve member deflects back and forth due to variations of the pressure of oil flowing through the outflow-adjusting hole 14', whereby the fan hunts. In addition, the centrifugal force acting on oil increases the oil pressure to hinder the valve member from closing the outflow-adjusting hole. When the engine is started or accelerated, the rotational speed of the sealed housing increases rapidly to thereby rotate the fan at a high speed, because a means for preventing oil from flowing into the outflow-adjusting hole is not mounted on the upstream side of the adjusting hole as viewed in the direction of rotation.